Urea Unfolding of Opsin in Phospholipid Bicelles

C Mckibbin, NA Farmer, PC Edwards, C Villa, PJ Booth

Research output: Contribution to journalArticle (Academic Journal)peer-review

17 Citations (Scopus)


Opsin is the unstable apo-protein of the light-activated G protein-coupled receptor rhodopsin. We investigated the stability of bovine opsin, solubilized in 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/detergent bicelles, against urea-induced unfolding. A single irreversible protein unfolding transition was observed from changes in intrinsic tryptophan fluorescence and far-UV circular dichroism. This unfolding transition correlated with loss of protein activity. Changes in tertiary structure, as indicated by fluorescence measurements, were concomitant with an approximate 50% reduction in -helical content of opsin, indicating that global unfolding had been induced by urea. The urea concentration at the midpoint of unfolding was dependent on the lipid/detergent environment, occurring at approximately 1.2 m urea in DMPC/1,2-dihexanoyl-sn-glycero-3-phosphocholine bicelles, while being significantly stabilized to approximately 3.5 m urea in DMPC/3-[(cholamidopropyl)dimethylammonio]-1-propanesulfonate bicelles. These findings demonstrate that interactions with the surrounding lipids and detergent are highly influential in the unfolding of membrane protein structure. The urea/bicelle system offers the possibility for a more detailed understanding of the structural changes that take place upon irreversible unfolding of opsin.
Translated title of the contributionUrea Unfolding of Opsin in Phospholipid Bicelles
Original languageEnglish
Pages (from-to)494 - 500
Number of pages6
JournalPhotochemistry and Photobiology
Volume85 (2)
Publication statusPublished - Mar 2009

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